166S drive always reports very high error levels

I have a JLMS XJ-HD166S with DS1E firmware, under Windows XP SP2. Until now I always could K-Probe scans with the limitations of a DVD reader, but it’s better than nothing and I can get an ideia of the burning quality.
But today, without no reason, and I haven’t changed anything on my system.
First I thought my NEC 2500 DVD was having some hardware problem and was burning bad. But then I scanned some DVD-R/+R discs that I had previously burned and scanned sucessfuly with low PI/PIF error levels.
Now the 166S reports always reports very high error levels, and I’ve tried several media, and I’m sure they’re OK.
All scans are very much the same, like this one:

Is my drive faulty? Or there is any other explanation?

This only enforces the fact that DVD-ROM drives are useless for scanning.

But until now I had some decent scans. Check this one (RICOHJPN2)